<style>
.input:focus {border: .05rem solid red;}
</style>
<div class="content">
  <div class="list">
    <div class="item">
      <div class="content">
        <div class="control">
          <label for="email">电子邮件</label>
          <input name="email" type="email" class="input" placeholder="example@email.com">
          <div class="help-text">点击并激活上面的电子邮件输入框</div>
        </div>
        <div><pre class="prettyprint"><code>&lt;div class=&quot;control&quot;&gt;
  &lt;label for=&quot;email&quot;&gt;电子邮件&lt;/label&gt;
  &lt;input name=&quot;email&quot; type=&quot;email&quot; class=&quot;input&quot; placeholder=&quot;example@email.com&quot;&gt;
&lt;/div&gt;</code></pre></div>
        <div><pre class="prettyprint"><code>.input:focus {
  border: .05rem solid red;
}</code></pre></div>
      </div>
    </div>
  </div>
</div>
